Preserving contours in dual pyramids

Pyramid schemes are described that make use of relations between the different resolutions of pictorial entities, such as intensity and edge. The presented system consists of a 3×3/2 intensity and a 2×2/2 curve pyramid. At every level, the two square grids are dual to each other. Contour operators generate the symbolic curve codes in the base of the curve pyramid. When the operators are moved several steps up and down in the curve pyramid, short contour segments are removed from the base. The remaining curves are used to preserve the contours at the reduced levels of the intensity pyramid. Experiences from different variants of the dual concept are reported